In general, you should dress as if you were going for a hike in the woods: wear sunscren, a hat, and layers to account for variable weather conditions, etc.

One key item to wear on the Intermediate and Advanced courses is: long pants or gaitors.

Some people wear ankle-length gaitors to keep gravel and debris out of their shoes while running.

Others wear knee-length gaitors (or pants) to protect their shins from being scratched by brush. Keep in mind that you'll likely be travelling off-trail -- and possibly through thick brush -- if you're on one of the Intermediate or Advanced courses (Orange, Green or Red).